Since the commit "8003c9ae204e: add APIC Timer periodic/oneshot mode VMX
preemption timer support", a Windows 10 guest has some erratic timer
spikes after few hours. As the uptime of the VM grows the spikes are
larger.
Here the results on a 150000 times 1ms timer without any load:
Before 8003c9ae204e | After 8003c9ae204e
Max 1834us | 86000us
Mean 1100us | 1021us
Deviation 59us | 149us
Here the results on a 150000 times 1ms timer with a cpu-z stress test:
Before 8003c9ae204e | After 8003c9ae204e
Max 32000us | 140000us
Mean 1006us | 1997us
Deviation 140us | 11095us
The root cause of the problem is starting hrtimer with an expiry time
already in the past can take a long time to trigger the timer function.
It can be solved by executing such past timers immediately, rather than
submitting them to hrtimer_start().
In case that the timer is periodic, set the new target expiration and
call hrtimer_start with it.
v2: Check if the tsc deadline is already expired. Thank you Mika.
v3: Execute the past timers immediately rather than submitting them to
hrtimer_start().
Cc: Mika Penttilä <mika.penttila@xxxxxxxxxxx>
Cc: Wanpeng Li <kernellwp@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Anthoine Bourgeois <anthoine.bourgeois@xxxxxxxxxxxxxxx>
---
arch/x86/kvm/lapic.c | 37 ++++++++++++++++++++-----------------
1 file changed, 20 insertions(+), 17 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 70dcb5548022..5b4455e13c29 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1463,23 +1463,6 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
local_irq_restore(flags);
}
-static void start_sw_period(struct kvm_lapic *apic)
-{
- if (!apic->lapic_timer.period)
- return;
-
- if (apic_lvtt_oneshot(apic) &&
- ktime_after(ktime_get(),
- apic->lapic_timer.target_expiration)) {
- apic_timer_expired(apic);
- return;
- }
-
- hrtimer_start(&apic->lapic_timer.timer,
- apic->lapic_timer.target_expiration,
- HRTIMER_MODE_ABS_PINNED);
-}
-
static void update_target_expiration(struct kvm_lapic *apic, uint32_t old_divisor)
{
ktime_t now, remaining;
@@ -1537,6 +1520,26 @@ static bool set_target_expiration(struct kvm_lapic *apic)
return true;
}
+static void start_sw_period(struct kvm_lapic *apic)
+{
+ if (!apic->lapic_timer.period)
+ return;
+
+ if (ktime_after(ktime_get(),
+ apic->lapic_timer.target_expiration)) {
+ apic_timer_expired(apic);
+
+ if (apic_lvtt_oneshot(apic))
+ return;
+
+ set_target_expiration(apic);
+ }
+
+ hrtimer_start(&apic->lapic_timer.timer,
+ apic->lapic_timer.target_expiration,
+ HRTIMER_MODE_ABS_PINNED);
+}
+
static void advance_periodic_target_expiration(struct kvm_lapic *apic)
{
apic->lapic_timer.tscdeadline +=
--
2.11.0
